Fig 6
a, b Photosynthetic capacity (A max ), c, d light compensation point (LCP) of photosynthetic net CO 2 uptake, e, f photosynthetic quantum yield (ϕ), and g, h carbon isotope discrimination (∆) of F. sylvatica and A. alba in relation to the specific leaf area (SLA) and chlorophyll-to-nitrogen ratio (Chl/N) in spring and summer 2017. The saplings of F. sylvatica and A. alba trees were excluded from these regressions. Axes of SLA were log transformed and axes of A max , LCP, and Chl/N were square root transformed to conform with assumptions of homoscedasticity. Regression lines were added when SLA or Chl/N had a significant effect (p < 0.05, see Table 2)
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While foliar photosynthetic relationships with light, nitrogen, and water availability have been well described, environmental factors driving vertical gradients of foliar traits within forest canopies are still not well understood. We, therefore, examined how light availability and vapour pressure deficit (VPD) co-determine vertical gradients (bet...
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... The time window that shows the largest r 2 indicates the likely time scale of light acclimation for Chl. We did not incorporate T and VPD into the correlation because there have been debates on whether these factors would impact Chl (Bachofen et al., 2020;Dusenge et al., 2020;Goto et al., 2021;Kong et al., 2021;León-Chan et al., 2017). Indeed, the r 2 values from the multiple regressions of Chl to PAR, T, and VPD show limited variation, indicating that the multiple regression approach is unsuitable for determining the temporal scale of Chl acclimation (Supporting Information S1: Figure 2). ...
Accurate estimation of photosynthesis is crucial for ecosystem carbon cycle modelling. Previous studies have established an empirical relationship between photosynthetic capacity (maximum carboxylation rate, V cmax ; maximum electron transport rate, J max ) and leaf chlorophyll (Chl) content to infer global photosynthetic capacity. However, the basis for the Chl‐V cmax relationship remains unclear, which is further evidenced by the temporal variations in the Chl‐V cmax relationship. Using multiple years of observations of four deciduous tree species, we found that V cmax and J max acclimate to photosynthetically active radiation faster (4–8 weeks) than Chl (10–12 weeks). This mismatch in temporal scales causes seasonality in the V cmax ‐Chl relationship. To account for the mismatch, we used a Chl fluorescence parameter (quantum yield of Photosystem II, Φ(II)) to tighten the relationship and found Φ(II) × Chl correlated with V cmax and J max ( r ² = 0.74 and 0.72 respectively) better than only Chl ( r ² = 0.7 and 0.6 respectively). It indicates that Φ(II) accounts for the short‐term adjustment of leaf photosynthetic capacity to light, which was not captured by Chl. Our study advances our understanding of the ecophysiological basis for the empirical V cmax ‐Chl relationship and how to better infer V cmax from Chl and fluorescence, which guides large‐scale photosynthesis simulations using remote sensing.
... In all plots, N tot was highest for both beech and fir in the open and lowest in the closed canopy, without significant differences between light categories and years. On all studied plots N tot was within the optimal thresholds 13-15mg/g for fir and 18-22mg/g for beech, as reported by Grassi and Bagnaresi (2001); Mellert and Göttlein (2012) or even above range reported by Yang et al. (2022) and Bachofen et al. (2020). The same trend was observed for LMA. ...
Predicting global change mitigations based on environmental variables, like temperature and water availability, although yielding insightful hypothesis still lacks the integration of environmental responses. Physiological limits should be assessed to obtain a complete representation of a species’ fundamental niche. Detailed ecophysiological studies on the response of trees along the latitudinal gradient are rare. They could shed light on the behaviour under different light intensities and other studied traits. The forests of the Dinaric Mountains and the Carpathians represent the largest contiguous forest complexes in south-eastern Europe. In uneven-aged Carpathian (8 plots) and Dinaric Mountain (11 plots) forests, net assimilation (Amax) and maximum quantum yield (Φ) were measured for beech and fir in three predefined light intensity categories according to the indirect site factor (ISF%) obtained by the analysis of hemispherical photographs in managed and old growth forests, all located above 800 m a.s.l. The measurements were carried out under fixed environmental conditions in each light category per plot for three consecutive years. Data from the last 50-year average period from the CRU TS 4.01 dataset were used for the comparison between Amax, Φ, and climate. The highest Φ for beech were observed in the central part of the Dinaric Mountains and in the south westernmost and northwesternmost part of the Carpathians for both beech and fir, while they were highest for fir in the Dinaric Mountains in the northwesternmost part of the study area. The Φ-value of beech decreased in both complexes with increasing mean annual temperature and was highest in the open landscape. For fir in the Carpathians, Φ decreased with increasing mean annual temperature, while in the Dinaric Mountains it increased with higher temperature and showed a more scattered response compared to the Carpathians. Short-term ecophysiological responses of beech and fir were consistent to long-term radial growth observations observed on same locations. The results may provide a basis and an indication of the future response of two tree species in their biogeographical range to climate change in terms of competitiveness, existence and consequently forest management decisions.
... The leaves of shade-tolerant species are generally more efficient at resource use than those of shade-intolerant species (Legner et al. 2014). Under low light conditions, to improve and optimize light harvesting, shade-tolerant species allocate more N to light-harvesting chlorophyll complex proteins, while less shade-tolerant species allocate more N to a key photosynthetic enzyme, Rubisco, and electron transport components (Niinemets and Tenhunen 1997;Evans and Poorter 2001;Bachofen et al. 2020). In shade intolerant species, electron transport capacity is optimized in terms of light availability, while for shadetolerant species, carboxylation capacity is optimized (Legner et al. 2014). ...
... Nitrogen is a major element of photosynthetic enzymes. Upper leaves are allocated more N because more light is available (Bachofen et al. 2020;Zhuang et al. 2021). Further, upper canopy leaves under intense light conditions can avoid damage with lower Chl leaf and higher Chl a:b ratios (Niinemets 2007;Lichtenthaler and Babani 2022). ...
Forest productivity is closely linked to seasonal variations and vertical differentiation in leaf traits. However, leaf structural and chemical traits vary among co-existing species, and plant functional types within the canopy are poorly quantified. In this study, the seasonality levels of leaf chlorophyll, nitrogen (N), and phosphorus (P) were quantified vertically along the canopy of four major tree species and two types of herbs in a temperate deciduous forest. The role of shade tolerance in shaping the seasonal variation and vertical differentiation was examined. During the entire season, chlorophyll content showed a distinct asymmetric unimodal pattern for all species, with greater chlorophyll levels in autumn than in spring, and the timing of chlorophyll per leaf area peak gradually decreased as shade tolerance increased. Chlorophyll a:b ratios gradually decreased with increasing shade tolerance. Leaf N and P contents sharply declined during leaf expansion, remained steady in the mature stage and decreased again during leaf senescence. Over the seasons, the lower canopy layer had significantly higher chlorophyll per leaf mass but not chlorophyll per leaf area than the upper canopy layer regardless of degree of shade tolerance. However, N and P per leaf area of intermediate shade-tolerant and fully shade-tolerant tree species were significantly higher in the upper canopy than in the lower. Seasonal variations in N:P ratios suggest changes in N or P limitation. These findings indicate that shade tolerance is a key feature shaping inter-specific differences in leaf chlorophyll, nitrogen, and phosphorus contents as well as their seasonality in temperate deciduous forests, which have significant implications for modeling leaf photosynthesis and ecosystem production.
... In addition, the leaf functional traits exhibiting low variation (leaf water content, δ 13 C and stomata width) are mostly related to water use, suggesting that the water-use strategies of F. tinctoria may have a low plasticity (Hao et al. 2011b). Light, water and nutrient are indispensable substances and resources for plants, and strongly affects the survival, growth and reproduction of plants (Bachofen et al. 2020). ...
Despite intensive studies on plant functional traits, the intraspecific variation and their co-variation at the multi-scale remains poorly studied, which holds the potential to unveil plant responses to changing environmental conditions. In this study, intraspecific variations of 16 leaf functional traits of a common fig species, Ficus tinctoria G. Frost., were investigated in relation to different scales: habitat types (hemiepiphytic and terrestrial), growth stages (small, medium and large) and tree crown positions (upper, middle and lower) in Xishuangbanna, Southwest China. Remarkable intraspecific variation was observed in leaf functional traits, which was mainly influenced by tree crown position, growth stage and their interaction. Stable nitrogen isotope (δ15N) and leaf area (LA) showed large variations, while stable carbon isotope (δ13C), stomata width and leaf water content showed relatively small variations, suggesting that light- and nitrogen-use strategies of F. tinctoria were plastic, while the water-use strategies have relatively low plasticity. The crown layers are formed with the growth of figs, and leaves in the lower crown increase their chlorophyll concentration and LA to improve the light energy conversion efficiency and the ability to capture weak light. Meanwhile, leaves in the upper crown increase the water-use efficiency to maintain their carbon assimilation. Moreover, hemiepiphytic medium (transitional stage) and large (free-standing stage) figs exhibited more significant trait differentiation (chlorophyll concentration, δ13C, stomata density, etc.) within the crown positions, and stronger trait co-variation compared with their terrestrial counterparts. This pattern demonstrates their acclimation to the changing microhabitats formed by their hemiepiphytic life history. Our study emphasizes the importance of multi-scaled intraspecific variation and co-variation in trait-based strategies of hemiepiphyte and terrestrial F. tinctoria, which facilitate them to cope with different environmental conditions.
... We assume that the limited ability to compensate for water loss may originate from an extensive evaporation from the bark wound, which can be several times higher than the water losses from the intact bark surface (Loram-Lourenço et al. 2022). In our experiment, the water loss from the wounded terminal branches may have been very high also due to the exposure to increased VPD levels and more intensive air circulation compared with the proximal organs at lower canopy levels (Hinckley et al. 2011, Ambrose et al. 2016, Bachofen et al. 2020. Water supply by transpiration flow to the distant terminal branches thus may not have been sufficient to support the increased evaporation demands of both bark wound and supported leaves. ...
Xylem transport is essential to the growth, development, and survival of vascular plants. Bark wounding may increase the risk of xylem transport failure by tension-driven embolism. However, the consequences of bark wounding for xylem transport are poorly understood. Here, we examined the impacts of the bark wounding on embolism formation, leaf water potential, and gas exchange in terminal branches of two diffuse-porous tree species (Acer platanoides L., Prunus avium L.). The effects of bark removal were examined on field-grown mature trees exposed to increased evaporative demands on a short-term and longer-term basis (6 h vs. 6 d after bark wounding). Bark removal of 30% of branch circumference had a limited effect on xylem hydraulic conductivity when embolized vessels were typically restricted to the last annual ring near the bark wound. Over the six-day exposure, the non-conductive xylem area had significantly increased in the xylem tissue underneath the bark wound (from 22–29% to 51–52% of the last annual ring area in the bark wound zone), pointing to gradual yet relatively limited embolism spreading to deeper xylem layers over time. In both species, the bark removal tended to result in a small but non-significant increase in percent loss of hydraulic conductivity compared to control intact branches six days after bark wounding (from 6% to 8–10% in both species). The bark wounding had no significant effects on midday leaf water potential, CO2 assimilation rates, stomatal conductance, and water use efficiency in leaves of the current-year shoot, possibly due to limited impacts on xylem transport. The results of this study demonstrate that bark wounding induces limited but gradual embolism spreading. However, the impacts of bark wounding may not significantly limit water delivery to distal organs and leaf gas exchange at the scale of several days.
... Leaves forming and aging throughout the canopy volume creates an important light gradient from the young to the old leaves that are nested within the vertical light gradient (Field and Mooney, 1983; Durand et al., 2020). Such differences contribute to the heterogeneity in the features of leaves leading to differences in physiological performance (Oren et al., 1998;Ewers et al., 2005;Bachofen et al., 2020). To get an integrated picture of whole-plant water consumption from the responses of single leaves within the canopy, both the age of leaf, leaf inclination in response to incident solar radiation and environmental heterogeneity within the canopies of individual plants should therefore be accounted for (Constable and Rawson, 1980;Sobrado, 1994;Matloobi, 2012). ...
Although stomata conductance (Gs) and transpiration (Tr) are
important for gas exchange (CO2 and H2O), none of the available studies have
considered variation in Gs and Tr between old and young leaves in savanna trees
such as (Combretum molle, Piliostigma thonningii and Balanites aegyptiaca). The
study aimed at addressing variability in Tr and Gs of three species and their
response to changes in canopy microenvironment. Measurements were conducted
in Ruma National park. Two treatments and three replications were used in the
experiment arranged in a completely randomized design. Results revealed that all
the three species recorded highest Tr and Gs in young leaves compared to older
leaves. P. thonningii exhibited the highest values followed by C. molle and B.
aegyptiaca with the least. Highest Gs of 1.092±0.73 μg cm-2 s-1 was recorded in
young leaves of P. thonningii. Similarly, highest mean Tr of 15.73±0.92 μg cm-2
s-1 was recorded in young leaves of P. thonningii followed by C. molle
(13.02±1.6 μg cm-2 s-1). There was no significant relationship (P<0.05) between
Tr of old leaves of all the species with leaf temperature. B. aegyptiaca, and C.
molle exhibited a positive relationship between Tr and VPD in old and young
leaves with highest coefficient of determination of R2=0.9 obtained in B.
aegyptiaca and P. thonningii. Our findings show that estimations of the rate of Tr
and Gs is species specific and relies on the microenvironment that the selected
leaf is exposed to as well as the age of the leaves. When modeling Tr and Gs from
humid tropical savanna trees, generalization of leaf physiological traits is likely to
present contradicting results that may underestimate or overestimate their gas
exchange attributes.
... However, even in these ecosystems, light availability within individual tree crowns can vary 5-20-fold (McGuire et al. 2001;Battaglia et al. 2003;Scholes et al. 2004). In addition to light, air temperature is characteristically higher at the top of the plant canopy compared with the bottom (Niinemets and Valladares 2004;Rambo and North 2008;Niinemets 2016b;Rey-Sánchez et al. 2016;Jucker et al. 2018;Bachofen et al. 2020;Vinod et al. 2023). The temperature gradients are particularly pronounced in tall tree canopies (e.g., Niinemets and Valladares 2004;Rambo and North 2008;Niinemets 2016b;Jucker et al. 2018;Bachofen et al. 2020), and less prominent in shorter grassland canopies (Sheehy et al. 1977;Fliervoet and Werger 1984;LeCain et al. 2015). ...
... In addition to light, air temperature is characteristically higher at the top of the plant canopy compared with the bottom (Niinemets and Valladares 2004;Rambo and North 2008;Niinemets 2016b;Rey-Sánchez et al. 2016;Jucker et al. 2018;Bachofen et al. 2020;Vinod et al. 2023). The temperature gradients are particularly pronounced in tall tree canopies (e.g., Niinemets and Valladares 2004;Rambo and North 2008;Niinemets 2016b;Jucker et al. 2018;Bachofen et al. 2020), and less prominent in shorter grassland canopies (Sheehy et al. 1977;Fliervoet and Werger 1984;LeCain et al. 2015). Air humidity also varies in plant canopies, decreasing with increasing canopy height in both woody and herbaceous stands, resulting in strong gradients in vapor pressure deficits (V D ) between canopy top and bottom (Fliervoet and Werger 1984;Niinemets and Valladares 2004;Rambo and North 2008;Niinemets 2016b;Rey-Sánchez et al. 2016;Jucker et al. 2018;Bachofen et al. 2020;Vinod et al. 2023). ...
... The temperature gradients are particularly pronounced in tall tree canopies (e.g., Niinemets and Valladares 2004;Rambo and North 2008;Niinemets 2016b;Jucker et al. 2018;Bachofen et al. 2020), and less prominent in shorter grassland canopies (Sheehy et al. 1977;Fliervoet and Werger 1984;LeCain et al. 2015). Air humidity also varies in plant canopies, decreasing with increasing canopy height in both woody and herbaceous stands, resulting in strong gradients in vapor pressure deficits (V D ) between canopy top and bottom (Fliervoet and Werger 1984;Niinemets and Valladares 2004;Rambo and North 2008;Niinemets 2016b;Rey-Sánchez et al. 2016;Jucker et al. 2018;Bachofen et al. 2020;Vinod et al. 2023). These modifications in canopy microclimate imply a faster transpiration rate (ε) at given stomatal conductance (g s , ε = g s V D ) in leaves exposed to higher light. ...
Leaf photosynthetic capacity (light-saturated net assimilation rate, AA) increases from bottom to top of plant canopies as the most prominent acclimation response to the conspicuous within-canopy gradients in light availability. Light-dependent variation in AA through plant canopies is associated with changes in key leaf structural (leaf dry mass per unit leaf area), chemical (nitrogen (N) content per area and dry mass, N partitioning between components of photosynthetic machinery), and physiological (stomatal and mesophyll conductance) traits, whereas the contribution of different traits to within-canopy AA gradients varies across sites, species, and plant functional types. Optimality models maximizing canopy carbon gain for a given total canopy N content predict that AA should be proportionally related to canopy light availability. However, comparison of model expectations with experimental data of within-canopy photosynthetic trait variations in representative plant functional types indicates that such proportionality is not observed in real canopies, and AA vs. canopy light relationships are curvilinear. The factors responsible for deviations from full optimality include stronger stomatal and mesophyll diffusion limitations at higher light, reflecting greater water limitations and more robust foliage in higher light. In addition, limits on efficient packing of photosynthetic machinery within leaf structural scaffolding, high costs of N redistribution among leaves, and limited plasticity of N partitioning among components of photosynthesis machinery constrain AA plasticity. Overall, this review highlights that the variation of AA through plant canopies reflects a complex interplay between adjustments of leaf structure and function to multiple environmental drivers, and that AA plasticity is limited by inherent constraints on and trade-offs between structural, chemical, and physiological traits. I conclude that models trying to simulate photosynthesis gradients in plant canopies should consider co-variations among environmental drivers, and the limitation of functional trait variation by physical constraints and include the key trade-offs between structural, chemical, and physiological leaf characteristics.
... 77 Leaves that are directly exposed to sunlight require higher levels of N to support efficient carboxylation compared to the shaded leaves. 83 The increased leaf N content indicates enhanced N metabolism under weak light conditions. Since N assimilation requires carbon for growth support, amino acids and other N reserves can also compensate for C deficiency to improve plant tolerance to low light conditions. ...
Physiological and molecular cascades regulating C and N distribution between source and sink organ. Cotton is used as a model plant to illustrate the interplay between carbon and nitrogen as numbered 1–4. Inorganic N (nitrate (NO3⁻) and ammonium (NH4+)) are taken up by the activities of N‐related transporters via the xylem vessels as indicated by the red arrows (1). Upon arrival at the source organ, the NO3⁻/NH4⁺ is assimilated into amino acids encoded by N assimilation enzymes (2). Also at the source leaf, plants assimilate photosynthetic C as sucrose and starch in the cytosol and chloroplast, respectively (3). Thus, the assimilated C and N in sucrose and amino acid forms are transported from the source (2) to the sink organ (flowers, cotton bolls, and fibre) by their respective transporters (the transporter family are indicated in the diagram above, since the activity of the family members varies among plant species) (4) as indicated by purple and brown arrows (for the sucrose and amino acid transport). Thus, this review describes the mechanisms of C and N transport from the primary assimilation site to the sink organ. Since plant biomass primarily depends on a balanced distribution of C and N among plant organs, the underlying physiological consequences of N status on carbon partitioning processes and vice versa were discussed. The potential roles of sucrose or nitrogen transporter activity in regulating C and N distribution processes were also elucidated. The latest multi‐omics techniques critical to identifying candidate genes involved in C and N metabolism were reviewed. image
... Canopy microclimate further strongly impacted transpiration as indicated by a strong effect of basal area on βVPD when soil water access was not limiting (Table 4). In (Bachofen et al., 2020). Consequently, the sensitivit y of stomata to changes in VPD is dampened in high basal area stands compared to low basal area stands Zhang et al., 2016). ...
Temperature rise and more severe and frequent droughts will alter forest transpiration, thereby affecting the global water cycle. Yet, tree responses to increased atmospheric vapour pressure deficit (VPD) and reduced soil water content (SWC) are not fully understood due to long‐term tree adjustments to local environmental conditions that modify transpiration responses to short‐term VPD and SWC changes.
We analysed sap flux density (SFD) of Fagus sylvatica, Picea abies, Pinus sylvestris and Quercus ilex from 25 sites across Europe to understand how daily variation in SWC affects the sensitivity of SFD to VPD (βVPD) and the maximum SFD (S95). Furthermore, we tested whether long‐term adjustments to site climatic conditions and stand characteristics affect βVPD and S95.
The studied species showed contrasting βVPD and S95 with the largest values in F. sylvatica, followed by Q. ilex, which surpassed the two conifers that showed low βVPD and low S95. We observed that βVPD and S95 dropped during days of low SWC in F. sylvatica, P. sylvestris and Q. ilex, but not in P. abies. Both βVPD and S95 were driven by tree height, and the temperature and precipitation at the sites. However, stand basal area was the most important driver of βVPD and S95, explaining 30% of their total variance.
Synthesis and applications: A future warmer and drier climate will restrict tree transpiration and thereby heavily affect the soil–plant‐atmosphere coupling. However, the effect of basal area, being the largest driver of tree transpiration sensitivity to vapour pressure deficit across a broad range of conditions, provides the opportunity to pre‐adapt European forests to future climate conditions. While stand thinning can increase the soil water availability for remaining trees, it also increases transpiration sensitivity to high air temperatures and may thereby amplify tree vulnerability to heat and drought.
... Precipitation is an important source of external water replenishment of terrestrial ecosystems, and its abnormal fluctuations can cause drought and consequent tree mortality [33]. SR (representing atmospheric drought) and VPD (to some extent) influenced plant growth, survival, and distribution, and the effects of these meteorological traits are not as well understood as those of precipitation and temperature [46,47]. Temperature is correlated to SR, VPD, and PET. ...
Frequent extreme climate events have significantly affected plant intrinsic water-use efficiency (iWUE) and forest nitrogen (N) availability. Understanding the coupling between climate seasonality and plant water, carbon, and nitrogen may provide insights into how plants respond to climate change. Here, we integrated ∆ 13 C and δ 15 N in woody plant leaves as a probe to elucidate the iWUE and N availability patterns of plants under global change and found that woody plants from sites with high climate seasonality, especially precipitation seasonality, tend to have improved iWUE and N availability compared with those with low seasonality. Specifically, high potential evapotranspiration, solar radiation, vapor pressure deficit, and low precipitation during the growth season are the driving factors. The intra-annual and annual climate explained 43% and 49% of ∆ 13 C and 40% and 53% of δ 15 N, respectively, suggesting that the intra-annual climate is at least as important as the annual climate. These results suggest that not only the direction (decrease vs. increase) of decadal climate should be counted but also the abnormal fluctuation of intra-annual should be considered. Climate seasonality is a more suitable ecological filter for determining plant distribution across terrestrial ecosystems.
